1. Field of the Invention
The present invention relates to programming phase change memory and, more specifically, maximizing the effective endurance of the phase change memory elements during memory programming.
2. Description of Background
There are two major groups in computer memory: non-volatile memory and volatile memory. Constant input of energy in order to retain information is not necessary in non-volatile memory but is required in the volatile memory. Examples of non-volatile memory devices are Read Only Memory (ROM), Flash Electrical Erasable Read Only Memory, Ferroelectric Random Access Memory, Magnetic Random Access Memory (MRAM), and Phase Change Memory (PCM). Non-volatile memory is memory in which the state of the memory elements can be retained for days to decades without power consumption.
On the other hand, volatile memory requires continual input of energy in order to retain information. Examples of volatile memory devices include Dynamic Random Access Memory (DRAM) and Static Random Access Memory (SRAM). DRAM requires the memory element to be repeatedly refreshed while SRAM requires a constant supply of energy to maintain the state of the memory element.
The present invention is directed to phase change memory. Phase change memory stores information in materials that can be manipulated into different phases. Each of these phases exhibit different electrical properties which can be used for storing information. The amorphous and crystalline phases are typically two phases used for binary storage (1's and 0's) since they have detectable differences in electrical resistance. Specifically, the amorphous phase has a higher resistance than the crystalline phase.
Chalcogenides are a group of materials commonly utilized as phase change material. This group of materials contain a chalcogen (Periodic Table Group 16/VIA) and another element. Selenium (Se) and tellurium (Te) are the two most common semiconductors in the group used to produce a chalcogenide when creating a phase change memory cell. An example of this would be Ge2Sb2Te5 (GST), SbTe, and In2Se3.
One drawback of phase change memory is degradation of the phase change material with repeated read-write phase change cycles. The phase change material may phase segregate, undergo local variations in stoichiometry, and the dopant atoms may redistribute themselves. Thus, it is desirable to devise a solution to prevent problems associated with repeated phase change cycles in phase change memory devices.